\documentclass{book}
\usepackage{array}

\begin{document}
\begin{center}
	\setlength\extrarowheight{5pt}
	\makebox[0pt]{%
		\begin{tabular}{ |>{\arraybackslash}m{1in} | >{\centering\arraybackslash}m{1in} | >{\centering\arraybackslash}m{1in} | >{\centering\arraybackslash}m{1in} | >{\centering\arraybackslash}m{1in} | @{}m{0pt}@{}}
			\cline{2-5}
			\multicolumn{1}{c|}{} & \multicolumn{2}{c|} {Probe}                            & \multicolumn{2}{c|} {Probe}                               \\[0.4cm]
			\cline{2-5}
			\multicolumn{1}{c|}{} & \multicolumn{1}{c|}{Pump} & \multicolumn{1}{c|} {Pump} & \multicolumn{1}{c|} {Pump} & \multicolumn{1}{c|} {Pump}   \\[0.4cm]
			\hline
			a                     & 5,0441                    & 1,9797                     & 4,6986                     & 2,9247                     & \\[0.4cm]
			\hline
			b                     & 1,0364                    & 1,0047                     & -1,2025                    & -0,9834                    & \\[0.4cm]
			\hline
			c                     & 0,5283                    & 0,0717                     & 0,1125                     & 0,3644                     & \\[0.4cm]
			\hline
			d                     & 0,2361                    & 0,1967                     & -0,1241                    & -0,3231                    & \\[0.4cm]
			\hline
			e                     & 0,0241                    & -0,0014                    & 0,0028                     & 0,0286                     & \\[0.4cm]
			\hline
			f                     & 0,0924                    & -0,0234                    & -0,1167                    & -0,1930                    & \\[0.4cm]
			\hline
		\end{tabular}}
\end{center}

\hrule

\end{document}
